In U.S. Pat. No. 4,360,728, Drexler discloses a data card writing and reading system in which a laser light source emits a beam directed to a card. A first servo controlled mirror is mounted for rotation in order to find the lateral edges of laser recording material on the card in a coarse mode of operation and then in a fine mode of operation identify data paths which exist predetermined distances from the edges. A second servo controlled mirror is mounted for rotation in order to scan the beam in a fine mode of operation along the length of the card. Coarse control of the lengthwise position of the card is achieved by motion of a movable holder supporting the card. When recording, the beam produces light scattering or absorbing pits representing data bits in the laser recording material. The data are read by a photodetector detecting differences in reflectivity between a pit and surrounding material using a reduced power laser beam.
In U.S. Pat. No. 3,654,624, Becker et al. disclose a laser recording system in which a flat elongated record strip is wound around the surface of a drum. The drum is rotated with respect to the laser beam during recording and reproducing operations. By means of a servo-controlled linear positioning mechanism, the laser beam is moved transversely to the direction of drum rotation to permit selection of any one of a large number of spaced parallel scan lines on the record strip.
In an application of card duplicating, such as for on-demand publishing, there is a need to record from about ten to a few thousand data cards, all containing the same or similar information. A typical card writer/reader has a recording speed of about 10,000 data spots per second. Thus, it would require about 30 minutes to fill a single card with 2 megabytes of data. Although lasers are capable of generating pulses at a rate exceeding 200,000 per second, the overall recording speed is reduced by the continuous accelerations and decelerations involved in card motion relative to a fixed laser, or vie versa. The need to synchronize the laser beam pulses with the speed and position of the card also reduces the recording speed.
In prior application Ser. No. 937,648 a data card recording system was disclosed which records identical data on each of a plurality of data cards supported around the circumferential surface of a drum. The drum is mounted for rotation and may have flanges set in the circumference for gripping the longitudinal ends of the cards. Alternatively, the drum may comprise a pair of concentric cylinders in which the cards ar mounted between the cylinders. A light source emits a light beam which is directed along an optical path to the cards. The drum may be transmissive to the light beam or have openings or transmissive windows where the card is mounted on the inside rather than on the outside of the drum. The system also includes a data control circuit in communication with a data source and having at least one memory location for storing a data segment to be recorded onto the data cards. A modulator, such as an acoustic-optical modulator, may be electrically connected to the data control circuit and positioned in the optical path to modulate the light beam in response to the data segment. Alternatively, a semiconductor laser may be directly modulated by current control methods. Each of the cards has a strip of laser recordable optical data storage material disposed thereon, so that as the drum rotates, the modulated beam produces data spots corresponding to the stored data segment in one of a plurality of parallel tracks on each of the data cards on the drum.
Tracks of data are aligned in the direction of drum rotation. The relative transverse position between the beam and the cards is movable, as by moving an element in the beam path, so that additional data segments may be recorded in multiple parallel tracks on each of the cards. The data control circuit in communication with a drive control synchronizes the light beam modulation rate to the drum speed. Recording is complete when the data cards are each filled with identical information or when all data segments have been recorded. A photodetector may be positioned for reading a track on a card, measuring changes in optical contrast defined by data spots formed on the track and thereby verify that data recording is accurate. The same or another photodetector may provide autofocus control of the light beam. The same or still another photodetector may provide servo tracking of the light beam.
While the above system duplicated cards very rapidly, the cards produced were not suited to all applications, particularly high speed reading. An object of the invention was to devise a high speed data card recording system optimized for producing cards suited for high speed reading.